Junction Field Effect Transistors (JFETs) are voltage-controlled semiconductor devices configured to control an electric current between a source electrode and a drain electrode by a gate voltage. Specifically, a JFET is a device that has a channel region between the source electrode and the drain electrode and in contact with a gate electrode, and that is configured to alter the thickness of a depletion layer in a pn junction formed by a gate semiconductor layer and a channel semiconductor layer, by a voltage applied to the gate electrode, thereby controlling a drain current flowing in the channel region.
Semiconductor devices using silicon as a semiconductor material prevail nowadays. In the case of silicon-based power semiconductor devices, device types to be used differ depending upon breakdown voltages of the devices: MOSFETs (metal/oxide/semiconductor field effect transistors) are the mainstream in low voltage systems where the device breakdown voltage is not more than 200 V; IGBTs (insulated gate bipolar transistors), thyristors, or the like are the mainstream in high voltage systems where the device breakdown voltage is higher than 200 V.
As for the JFETs, static induction transistors (SITs), a type of JFETs, have been developed and manufactured as power semiconductors. The SITs have the device structure similar to the JFETs; precisely, the static characteristics of the JFETs are the pentode characteristics with saturation, whereas the static characteristics of the SITs are the triode characteristics characterized by unsaturation.